The present invention relates to a method for recovering fuel vapor during an onboard refueling operation, more particularly, a method for operating an onboard refueling vapor recovery (ORVR) system of an automotive vehicle.
Increasingly stringent environmental standards have resulted in regulations necessitating a significant reduction in fuel vapors escaping from a vehicle fuel tank during refueling. These regulations generally strive to essentially eliminate fuel vapor escaping into the atmosphere during refueling. The resultant emission control systems are referred to as onboard refueling vapor recovery (ORVR) systems.
In such an ORVR system, the filler neck of the fuel system is designed to a diameter to create a seal in the filler neck to prevent vapors from escaping from the fuel tank through the filler neck. During refueling, the fuel volume within the tank increases, thereby reducing the available space for fuel vapors. The pressure created by filling the tank causes the fuel vapors to exit through an exhaust port to a purge canister. The purge canister typically includes a charcoal element to capture hydrocarbons while releasing filtered vapors into the atmosphere.
In a typical ORVR system, a control valve is placed in the flow path between the fuel tank and the purge canister. The primary purpose of such a control valve is to enable the transmission of vapor while preventing the transmission of liquid fuel to the purge canister. In case of liquid fuel reaching the purge canister, a situation referred to as carryover, fuel can collect within the purge canister. Because the canister may later be purged to provide fuel to the vehicle via the intake manifold, excessive fuel carryover may cause liquid fuel to exit the fuel system or interfere with engine operation.
Typically ORVR control valves are of mechanical nature. They are normally open and thus provide a flow path between the fuel tank and the purge canister. However, these normally open valves must be adaptable to close off the flow path between the fuel tank and the purge canister during conditions such as vibration, slosh, and vehicle tilting which might otherwise result in a carryover condition. Typical valves include a buoyant member with a bias toward an open position. The valve is responsive to slosh, vibration, and tilting conditions to close the vapor passage. However, such valves are often slow to respond and include many moving parts which eventually deteriorate, thereby adversely affecting operation of the valve.
U.S. Pat. No. 6,601,617 to Enge proposes to provide the ORVR system with an electronic control valve to selectively enable the passage of fuel vapor from the fuel tank to the purge canister during predetermined conditions. Furthermore, a method is proposed for controlling the electronic control valve which enables vapor to pass from the fuel tank to the purge canister only during predetermined conditions.
This invention is also directed to a method for recovering vapor during an onboard refueling operation in a vehicle. The method includes providing a flow path between a fuel tank and a purge canister. The method also includes providing a fueling event sensor for detecting at least one of the introduction of fuel into the fuel tank or the introduction of a filler nozzle into a filler neck of the fuel tank, defined as a fueling event. The method further includes providing an ORVR valve in the flow path and actuating the ORVR valve in accordance with the output of the fueling event sensor to selectively open and close the flow path.
A problem associated with electronic ORVR valves controlling the shutoff level, and indeed of the method as disclosed in U.S. Pat. No. 6,601,617, is a fuel spit-back. The closing of all communication to the purge canister at the end of a refueling event will in many cases result in liquid fuel being ejected out of the fill head and, in some cases, onto the operator. It is clear that this is both a safety and an environmental concern and must be avoided.
It is therefore an object of the present invention to provide an improved method for recovering fuel vapor during an onboard refueling operation wherein spit-back is prevented.